1. Field of the Invention
The present invention relates to a novel headlamp for vehicles, and, more particularly, to a novel vehicular headlamp which can emit a beam that illuminates so-called overhead signs, which are placed over an expressway or the like.
2. Description of the Related Art
Drivers have no particular problems recognizing overhead signs, which are written by luminous paint or the like, at night, but may overlook non-luminous overhead signs at night unless sufficient light is around.
To cope with the above situation, some beams from the headlamp may be used to illuminate overhead signs.
FIG. 1 shows the luminous intensity distribution a of a low beam, which should illuminate a region b of about 2 to 5 degrees above the horizontal line.
To fulfill the requirement, a prism d which refracts light upward may be formed at the inner wall of a lens c at a position above the center thereof, as shown in FIG. 2. Parts e' of light beams e which travel nearly parallel to or slightly downward to the optical axis x--x are refracted upward by this prism d to illuminate overhead signs.
The structure using the prism d formed on the inner wall of the lens c to provide beams to illuminate overhead signs raises several problems.
First, the portion of the lens c where the prism d is formed becomes too thick, causing the deterioration of the designability of such lenses.
There is another problem concerning the dazzling light to approaching vehicles from opposite direction. If light is irradiated to the region g between the aforementioned region b and the cut line f of the low beam a, it will dazzle the driver of an approaching vehicle so that no beams should be irradiated in this region g. According to the structure shown in FIG. 2, however, the prism rising portion h at the upper end portion of the prism d refracts the incident beams e to yield upward beams i which may dazzle the driver of an approaching vehicle.